Shear-sensitive plugging fluid for plugging and a method for plugging a subterranean formation zone

Abstract

A plugging fluid for plugging a subterranean formation zone surrounding a drill hole comprises an emulsion comprising a dispersed aqueous phase containing an aqueous base and a continuous hydrophobic phase containing a polymer consisting of a grafted cellulose ether derivative, a surfactant and a crosslinking activator of the polymer. The polymer is preferably 2-hydroxyethyl cellulose grafted with vinyl phosphonic acid. Upon shearing, preferably through the drilling bit, the emulsion inverts so that the rupture of the emulsion droplets releases the crosslinking activator into the water phase thus forming a gel structure.

What is claimed is:  
     
       1. A plugging fluid for plugging a subterranean formation zone surrounding a drill hole essentially consisting of an emulsion comprising a dispersed aqueous phase containing an aqueous base and a continuous hydrophobic phase containing a polymer consisting of a grafted cellulose ether derivative, a surfactant and a crosslinking activator of the polymer. 
     
     
       2. The plugging fluid of  claim 1 , wherein the polymer is a grafted hydroxyalkylcellulose polymer derivative graft polymer. 
     
     
       3. The plugging fluid of  claim 2 , wherein the polymer is 2-hydroxyethyl cellulose grafted with vinyl phosphonic acid. 
     
     
       4. The plugging fluid of  claim 3 , wherein the ratio of 2-hydroxyethyl cellulose to vinyl phosphonic acid monomers in the graft polymer ranges from about 5% to about 20%. 
     
     
       5. The plugging fluid of  claim 1 , wherein the crosslinking activator of the polymer are selected from the groups consisting of compounds providing iron III, boron, titanium IV, zirconium IV, aluminum III and antimony V ions; compounds containing divalent calcium and magnesium ions, amines, acetates, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium acetate, ammomia, ammonia generating compounds, chelating agents, sodium gluconate, sorbitol, and glycerol and mixture thereof. 
     
     
       6. The plugging fluid of  claim 1 , wherein the oil is present in a concentration of from about 5 to about 70 wt %, and the water is present in a concentration of from about 30 to about 95 w %. 
     
     
       7. A plugging fluid comprising from about 10 to 25 wt % of diesel oil, 0.1 to 3 w % of a polyamide derivative, 0.1 to 5 w % of a 2-hydroxyethylcellulose grafted with vinyl phosphonic acid, 70 to 90 wt % of fresh water, 0.5 to 1.5 w % of magnesium oxide, 0.5 to 1 w % of sodium carbonate, 0.1 to 1 w % of sodium tetraborate pentahydrate and 0.1 to 1 w % of the hydroxyethylethylene-diaminetracetic acid. 
     
     
       8. A plugging fluid for plugging a subterranean formation zone surrounding a drill hole essentially consisting of an emulsion comprising a dispersed aqueous phase containing an aqueous base and a continuous hydrophobic phase containing a polymer consisting of a grafted cellulose ether derivative, a surfactant and a crosslinking activator of the polymer, wherein said crosslinking activator comprises an admixture consisting of magnesium oxide, sodium carbonate, hydroxyethylethylene-diaminetriacetic acid, and sodium tetraborate.